It is known in the art to use plastic trays with a large number of molded depressions arrayed thereon. Each depression has a drainage hole in the bottom to form a germination cell. The cells are filled with a growth medium and seeds. The trays are stacked in a controlled environment germination chamber for a few days, then put in the greenhouse until the seedlings are ready for transplanting. For example, U.S. Pat. No. 4,769,946 to P. de Groot discloses such a tray. De Groot carefully limits the ventilation to the drainage hole area, by using small holes 42, so as to conserve moisture and encourage maximum germination. However, trays of this design allow the seedling roots to grow down through the drainage hole and spread outward, thus, locking the new and fragile plant into the germination cell.
Efficient farming techniques utilize seedling planting machines, such as shown in U.S. Pat. No. 4,970,972 to Williames. These machines typically eject the seedlings from the germination cells with a plunger that pushes up from the bottom of the tray so as to slide the plant, along with its surrounding growth medium, out of the tray and onto a suitable conveyor that carries the plant to the ground and plants it. If the plant has roots spreading out from the drainage hole that grasp the underside of the cell, substantial damage may be done to the seedling during this forcible ejection.
One prior art solution to this problem is disclosed in U.S. Pat. No. 4,144,672 to Gradwell et al. A tray using cells with break away bottoms is shown. This approach is expensive because the tray is destroyed after one use. Another solution is shown in U.S. Pat. No. 4,197,674 to Blackmore, which teaches cells having yieldable flap members in the bottom that bend out of the way of an ejection plunger. This method is also less than satisfactory because the flaps can clog with dirt, permanently distort after use, and still damage the roots of the seedlings that grow through the flap forming slits. The present invention avoids these problems with a tray designed to be especially suited to handling by machine.